In the early days of the great war only an occasional flash of news was received about the French and Russian aero-military operations or those of the German corps along the Russian and French frontiers. It was difficult to imagine that they were idle, for the German-Russian and the French-German frontiers had been the locations of many military aeronautical camps or fortresses. These were described at the outbreak of hostilities as follows: "Along the German frontier facing Russia are the important aero centers of Thorn and Graudenz, while the nearest aero base in Russia is at Riga, farther north. "Against German invasion there are French centers at Verdun, Nancy, Luneville and Belfort. The most important is at Belfort. Sixty miles from the Belgian frontier and 170 miles from Liege is the great center at Rheims, with the even more important base at Chalons-sur-Marne only twenty-five miles distant. "Seventy-five to 100 miles is the scouting range of the military aeroplanes, while the dirigibles will scout 500 to 1,000 miles from the base, according to the duration efficiency. The Zeppelins might, taking some risk, travel even farther. With this taken into consideration, the fact that there are only two German aero centers on the French frontier--Aix-la-Chapelle and Metz--is not very significant. The range of the Vosges occupies the territory where there is no aero center. "Back of the mountains, along the Rhone from Dusseldorf to Strasbourg, there are a dozen aero stations, some of them devoted to aeroplanes and dirigibles, others to dirigibles alone. "The latest data show that Germany has sixty stations, including private dirigible hangars, while France has thirty, in most cases of greater extent than those in Germany, Russia, eight months ago, had ten, but it is believed that this number has been increased twofold since that time. [Illustration: HOW GERMAN EMPIRE IS FORTIFIED AGAINST AERIAL ATTACKS. CENTERS FROM WHICH KAISER WILLIAM'S DIRIGIBLE AND AEROPLANE FLEETS OPERATE. ONLY THOSE CITIES THAT HAVE AERODROMES ARE SHOWN ON THIS MAP. SEVERAL BELGIAN AND FRENCH AERODROMES ALSO ARE SHOWN.] "The two principal Belgian centers are at Brasschaet, near Antwerp, and Etterbeck, near Brussels. The aviators operating in the early engagements have undoubtedly flown down from Brussels and are in temporary camp at Liege. There are probably not more than four Belgian escadrilles, or little fleets of four machines each, on the scene, while Germany's force is supposedly greater." CHAPTER XVIII BATTLE OF THE AISNE _Most Prolonged Encounter in History Between Gigantic Forces--A Far-Flung Battle Line--Germans Face French and British in the Aisne Valley and Fight for Weeks--Mighty Armies Deadlocked After a Desperate and Bloody Struggle_.